GRAPHIC: Alaska’s record heat a killer for some salmon, researchers say

About 800 otherwise healthy salmon were found dead in a river

GRAPHIC: Alaska’s record heat a killer for some salmon, researchers say
Chum salmon are shown here in a 2016 file photo. A recent trip down a river found a disturbing number of chum salmon dead. Researchers suspect the high water temperature caused the deaths. (AP Photo/Becky Bohrer) (Source: Becky Bohrer)

(CNN) - Scientists are blaming rising temperatures for reduced salmon populations in parts of Alaska.

Researchers on a river expedition last month found more than 800 dead chum salmon.

When they inspected the fish, they couldn't find any signs of parasites or infection.

Many of the salmon were also carrying healthy eggs.

Researchers concluded record high temperatures in the water was responsible. Stream temperatures near anchorage surpassed 76 degrees this year for the first time since record keeping began in 2002.

“It will be hard to determine the influence this die-off event will have on the future of the population, but we know salmon are resilient creatures that have rebounded quickly before - especially Yukon chum,” researcher Stephanie Quinn-Davidson said in a social media post. “Still... it was hard to see all these seemingly perfectly healthy salmon just dead.”

Warmer water makes it difficult for salmon to absorb the oxygen they need to breathe.

Ecologists worry reduced salmon populations will work their way up the food chain and impact animals that eat them, like orca whales.

GRAPHIC WARNING: Some people may find the photos embedded in the social media post below disturbing.

A fishery in Bristol Bay, Alaska, is reporting the opposite.

The largest sock-eye salmon fishery in the world is reporting a boom in the number of fish it is seeing return.

Sometimes my job is pretty cool. I had the opportunity to boat down a remote stretch of the Koyukuk River a week ago....

Posted by Stephanie Quinn-Davidson on Friday, August 2, 2019

Copyright 2019 CNN. All rights reserved. Gray Television Group contributed to this report.